I'm looking to replace my Top Fin 7.5 watt heater for my 3 gallon tank. I was looking to upgrade for a 10 watt heater. Any good recommendations?

The reason I want to replace the heater is because recently I've been noticing my heater not doing it's job as it should with holding temps between 72 - 75 degrees. Some days it goes down to 70; other times slightly above 70degrees - no nearer to 75 degrees. I think my heater is starting to konk out on me.